1. Field of the Invention
The present invention relates generally to the field of linear motion devices and more particularly to a pneumatic or rodless cylinder having a carriage moveable relative to a body and a bearing means for supporting and guiding reciprocal movement of the carriage relative to the body.
2. Description of the Prior Art
A variety of linear motion devices currently exist in the art. Many are of the type which include a body, a carriage moveable relative to the body and bearing or a support means positioned between the carriage and the body for purposes of supporting and guiding the carriage during movement relative to the body. Pneumatic or rodless cylinders represent one such form of linear motion device. These devices generally include an elongated cylinder body, a piston reciprocally moveable within the cylinder body and a carriage connected to the piston either directly or indirectly for transferring reciprocal movement of the piston to a workpiece. Such devices also include various bearing or other means for supporting and guiding the carriage during its reciprocal movement relative to the cylinder body.
One such means is shown in U.S. Pat. No. 4,724,744 issued to Rosengren in which a pair of integral arms extend outwardly from the carriage and embody a pair of low friction rods for sliding movement relative to a bearing groove in the outer side surfaces of the cylinder. A further guide and support mechanism is illustrated in U.S. Pat. No. 4,878,390 issued to Hauser. Hauser discloses a linear positioning apparatus having a cylinder body, a carriage moveable relative to the body and a bearing means comprising a series of recirculating ball bearings for guiding and supporting the carriage relative to the cylinder body.
Regardless of the particular bearing means utilized to support movement of the carriage relative to the body, the selection and design of such bearing means necessarily involves the consideration of several factors including the nature of the cylinder body, the method by which such body is manufactured, the reaction of the body to dynamic forces during operation, the tolerances achievable with a certain cylinder body design, and the tolerances needed for a particular bearing design.
Pneumatic or rodless cylinders of the type to which the present invention has particular application, commonly embody cylinder bodies which are relatively long compared to the carriage dimensions. It is not uncommon for such cylinder bodies to be 20 feet long or longer. This makes it extremely difficult to maintain close tolerances along the entire body length. Further, most of these elongated bodies for these pneumatic cylinders are extruded rather than machined. This further compounds the problem of maintaining close tolerances. Still further, pressures within the cylinder which drive the piston cause the cylinder to repeatedly expand and contract during reciprocal movement of the piston, thus presenting further problems with respect to establishing and maintaining tolerances.
Accordingly, there is a need in the art for a linear motion device and more particularly for a pneumatic or rodless cylinder device having an improved bearing support structure which minimizes the need to maintain close tolerances during manufacture of the component parts, but which still facilitates easy assembly of the device with the desired close tolerances.